const fs = require('fs');

function myReadfile(filename) {
    return new Promise((resolve, reject) => {
        fs.readFile(filename, 'utf-8', (err, data) => {
            err ? reject(err) : resolve(data.length);
        })
    }).catch(err => {
        console.log(err);
    })
}

async function abc() {
    let r1 = await myReadfile('./files/aa.txt');
    let r2 = await myReadfile('./files/b.txt');
    let r3 = await myReadfile('./files/c.txt');
    console.log(r1);
    console.log(r2);
    console.log(r3);
}
abc();